1. Field of the Invention
The present invention relates to an autofocus system, and in particular to an autofocus system in which an AF area, a range to be targeted by focusing in autofocusing (AF) within the image-taking range of a camera, is displayed in a view finder or the like of the camera.
2. Description of the Related Art
In an image-taking system which converts the image of a subject to an electric signal (an image signal) by an image-taking element (such as a CCD), like a TV camera, a contrast method is generally adopted as an autofocus (hereinafter referred to as AF) method. The contrast method is a method in which the contrast of the image of a subject is detected from an image signal (a picture signal) of the image of the subject acquired by the imaging element, and focusing is automatically performed to obtain the best focus state by controlling the focus of a photographing lens (a focusing lens) so that the contrast becomes the highest.
In the contrast method AF, the whole image-taking range of a camera is not targeted by focusing in AF, but only a subject within a partial range of the image-taking range is targeted by focusing in many cases. For example, from the image signal of a subject image effectively taken by an image-taking element, the image signal within a predetermined range targeted by AF is extracted, and focusing is controlled so that the contrast of the image becomes highest based on the image signal within the extracted range. Thereby, the target of AF is limited to a subject within the partial range. In this specification, the range targeted by AF is referred to as an AF area, and a frame indicating the range of the AF area (the outline of the AF area) is referred to as an AF frame.
For example, there is also proposed an autofocus system in which the position and the like of the AF area can be changed by an operator's operation, and the range of the AF area is displayed by an AF frame or the like on the screen of a view finder, as in Japanese Patent Application Laid-Open No. 2002-365519.